Lithium accumulator and the method of producing thereof

ABSTRACT

A lithium accumulator includes at least two three-dimensional electrodes separated by a separator and encased together into an accumulator body with an electrolyte that is a non-aqueous solution of a lithium salt in an organic polar solvent. The two electrodes have a minimum thickness of 0.5 mm each. At least one electrode is a homogenous, compressed mixture of an electron conductive component and an active material. The active material is capable of absorbing and extracting lithium in the presence of electrolyte. The porosity of the pressed electrodes is 25 to 90%. The active material has morphology of hollow spheres with a wall thickness of maximum 10 micrometers, or morphology of aggregates or agglomerates of maximum 30 micrometers in size. The separator includes a highly porous electrically insulating ceramic material with open pores and porosity from 30 to 95%.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is the National Stage of PCT/CZ2009/000112 filed onSep. 18, 2009, which claims priority under 35 U.S.C. §119 of CzechRepublic Application No. PV 2008-572 filed on Sep. 19, 2008, thedisclosure of which is incorporated by reference. The internationalapplication under PCT article 21 (2) was published in English.

FIELD OF THE INVENTION

The invention relates to a lithium accumulator including at least twothree-dimensional electrodes separated by a separator and encasedtogether with an electrolyte, comprising a non-aqueous solution of alithium salt in an organic polar solvent, into an accumulator body.Further, the invention relates to a method of producing lithiumaccumulator with a specific type of three dimensional electrodes.

BACKGROUND OF THE INVENTION

The lithium cells have been intensively developed during the recent twodecades enabling thus existence of many portable devices. Neverthelessthe growing demands for higher capacity and safety of lithium batteriesdo not always comply. This slows down progress of many applications,including the substitution of lead-acid accumulators with lithiumaccumulators possessing higher voltage, or development of largebatteries for electro mobiles and energy storage.

The prior art technologies using graphite as an active material for thenegative electrode are not able to ensure safety of a battery with theweight exceeding 0.5-1 kg. The efforts to increase the size of this typeof accumulators encounter many problems such as overheating,intermediate layer on the graphite, swelling, development of metallithium on the graphite surface and a risk of explosion or fire. Thesesafety problems push the large lithium accumulators beyond the limits ofacceptability.

Technologies substituting graphite with a different material, e.g.lithium titanate spinel Li₄Ti₅O₁₂ (LTS) strongly improve the safetyparameters of lithium batteries, but on the other hand, theysignificantly decrease the cell voltage.

The lithium batteries manufactured on this basis meet the safety demandsfor use in electro mobiles, but the weight parameters of such batteriesdon't allow their easy use in small vehicles.

All rechargeable lithium accumulators manufactured today are based onplanar electrodes, where a mixture of an active material, conductivecarbon and organic binding agent are laminated in a thin layer onto aconductive foil, usually aluminum or copper (current collector). Thethickness of these planar electrodes usually does not exceed 200micrometers. The positive and negative electrodes are stacked togetherseparated by a thin layer of an electrically insulating material,usually a perforated foil made of an organic polymer—separator. Thestacked thin-film electrodes insulated by the separators are thenpressed together, placed into the accumulator package and the spaceinside the accumulator is filled with an electrolyte. A non-aqueoussolution of lithium salts is used as an electrolyte. In connection withsuch devices based on the planar electrodes, it is most important toprevent the growth of lithium metal during the charging and dischargingprocess e.g. when the charging or discharging is too fast. The lithiummetal develops on electrodes in the form of dendrites, which overgrowthrough the separator and cause an electric shortage between bothelectrodes. Any use of metal lithium as a negative electrode in theplanar thin-film configuration accumulator is impossible for the samereason.

One type of a cell with thin-film planar electrodes is described indetail in U.S. Pat. No. 6,197,450. Despite its increased volumetriccapacity, this type is affected by inherent properties of planarelectrodes as described above.

One of possible compositions of a lithium battery with a thin-filmplanar electrode configuration is described in US. pat. application2007/0092798. Active nano-materials are used as a component of theelectrodes. The battery cell arranged in planar configuration shows arelative low volumetric capacity, which is further limited by the typeof cathode material.

Another US pat. application 2007/0134554 teaches a carbon electronconductor deposited on solid particles of a specific active material.The carbon improving the conductivity of the active material is to beformed directly on the surface of the active material using a rathercomplicated process of pyrolysis.

EP1244168A discloses the formation of thin layers of an electrochemicalcell by coating a suitable substrate with a paste comprising the activematerial, organic binders and conductive carbon without application of asintering process. The calculation of a model example 8, where aseparator of 50-90% porosity is used, shows a gradient of theelectrode's voltage with the electrical potential sharply dropping downwith the increasing thickness of the electrode. Based on this fact, itis to be understood that the disclosed network can not be used for theformation of electrodes of higher thickness, for example exceeding 0.5mm.

SUMMARY OF THE INVENTION

It is a primary object of the invention to provide a lithium accumulatorwith extended energy storage capacity and thickness of individualaccumulator components, which can operate in a wide electric potentialrange.

Another object of the invention is to achieve the highest voltage of theaccumulator and a considerable increase of the energy density.

Still another object of the invention is to provide an accumulator thatmay be used not only for high capacity button batteries andmicro-electric mechanic systems but also as a high energy densityaccumulator designed for car industry, energy storage, etc.

Further object of the invention is to provide a simple low-costaccumulator manufacturing process.

The objects of the present invention can be achieved and the describeddeficiencies overcame by a lithium accumulator including at least twothree-dimensional electrodes separated by a separator and encasedtogether with an electrolyte, comprising a non-aqueous solution of alithium salt in an organic polar solvent, into an accumulator bodycharacterized by that the two electrodes have a minimum thickness of 0.5mm each, of which at least one electrode comprises a homogenous,compressed mixture of an electron conductive component and an activematerial, capable to absorb and extract lithium in the presence ofelectrolyte, wherein the porosity of the pressed electrodes is 25 to90%, the active material has morphology of hollow spheres with a wallthickness of maximum 10 micrometers, or morphology of aggregates oragglomerates of maximum 30 micrometers in size, while the separatorconsists of a highly porous electrically insulating ceramic materialwith open pores and porosity from 30 to 95%.

Hereinafter, other advantageous embodiments of the invention includingmodifications, specific details and the method of production of thelithium accumulator are described.

The electron conductive component, the active material and the separatorare inorganic materials free of organic binders. This feature of theinvention is based on a new knowledge discovered in the course of makingthis invention that any presence of organic binders in said componentsadversary affects the diffusion of lithium ions within layers ofthickness exceeding several micrometers. Advantageous manufacturing bypressing creates accumulators that do not require any organic binders ofany kind and are vibration resistant.

The electron conductive component may be selected from a groupconsisting of a conductive carbon and its modifications, conductivemetals and electrically conductive oxides.

Usually, but without limitations, the active material can be selectedfrom the group consisting of mixed oxides or phosphates of lithium,manganese, chrome, vanadium, titanium, cobalt, aluminum, nickel, iron,lanthanum, niobium, boron, cerium, tantalum, tin, magnesium, yttrium andzirconium.

In a thin-film electrode, the particles of the active material have,within the scope of their usable capacity, the ability to completelyabsorb and extract lithium ions in the time interval of up to 20minutes.

The active material preferably consists of nanoparticles of doped andundoped spinels of lithium manganese oxide or lithium titanium oxidesized up to 250 nm.

The positive electrode comprises 40-85 wt % of the active material andoptionally a current collector in the form of expanded foil, net, grid,wire, fibers or powder.

The current collector is selected from a group consisting of aluminum,copper, silver, titanium, silicon, platinum, carbon or a material stablewithin the voltage window of the particular cell.

The electrode consists of a compressed, homogenous mixture of an activematerial, electron conductive component and a current collector.

The separator is a bulk layer or sheet of a highly porous powder of aceramic material, advantageously based on Al₂O₃ or ZrO₂.

Preferably, the separator may have a non-directional morphology of apyrolyzed product or nonwoven glass or ceramic fibers with an open typeof porosity, and may be made by compressing the powder of a pyrolyzedproduct or ceramic nonwoven fibers into a bulk layer. The thickness ofthe separator is ranging from 0.1 mm to 10 mm and the separator can becreated by compressing the powder directly onto the electrode, or it canbe separately pressed into a sheet, often a tablet, optionally thermallytreated, and then placed onto the electrode.

Both these morphologies of the fully inorganic separator, together withits thickness, which is many times higher compared to the separators ofthe previous art, enable the use of lithium metal as a negativeelectrode. This extends the voltage and the energy storage capacity ofthe lithium accumulator up to the theoretical possibilities.

The negative electrode preferably consists of lithium metal, which maybe in the form of a lithium sheet or a foil, or a combination of acompressed lithium sheet or foil and dendrites, or preferably lithiumdendrites as such. The dendritic form of lithium may be made “in situ”from the lithium foil or sheet by cycling of the lithium accumulator.Moreover, the size of dendrites and their surface can be modified byaddition of another compound, e.g. conductive carbon, or by theelectrolyte composition, or by mixing certain substances into theelectrolyte, e.g. stable phosphates.

The use of metal lithium, advantageously in its dendritic form, stronglyreduces the weight and size of the lithium accumulator and in theembodiments described herein; this form simultaneously increases theaccumulator safety in comparison with those containing graphite. To thiseffect, the combination of lithium metal dendrites with the abovedescribed organic free separator is used. The separator prevents lithiumdendrites from penetrating through it, so the dendrites may be used as anegative electrode. Moreover, said combination provides for a highsafety of the accumulator in the event of short-circuit.

The electrolyte lithium salt is preferably selected from the groupconsisting of LiPF₆, LiPF₄(CF₃)₂, LiPF₄(CF₄SO₂)₂, LiPF₄(C₂F₅)₂,LiPF₄(C₂F₅SO₂)₂, LiN(CF₃SO₂)₂, LiN(C₂F₆SO₂)₂, LiCF₃SO₃, LiC(CF₃SO₂)₃,LiBF₄, LiBF₂(CF₃)₂, LiBF₂(C₂F₅)₂, LiBF₂(CF₃SO₂)₂, LiBF₂(C₂F₅SO₂)₂ andLiClO₄. The electrolyte may further contain modification agentsimproving accumulator functions at high temperatures and/or removingdecomposition products and/or protecting the accumulator fromovercharging and/or substances controlling the size of metal lithiumdendrites.

According to one embodiment of the invention, the lithium accumulatorcomprises a hollow body having an upper opened part and a lower part toform a first pole of the accumulator, a first electrode situated in thelower part of the body and being in electrical contact with an internalsurface of the body, a second electrode in the upper part separated fromthe internal surface of the body by an insulating insert, a separatorplaced between the first electrode and the second electrode, a capclosing the upper opened part and being in electrical contact with thesecond electrode to form a second pole of the accumulator, a sealingcover for insulating the cap from the body.

According to another embodiment, the lithium accumulator comprises anupper body and a lower body joined together both defining an internalaccumulator space and connected to the first pole of the accumulator, afirst electrode pressed into the internal space of the bodies to form acentral cavity inside and being in electrical contact with the bodies, asecond electrode located inside the central cavity, the second pole ofthe accumulator being in electrical contact with the second electrodeand extending outside the accumulator body and separators dividing thefirst electrode from the second electrode.

According to still another embodiment, the lithium accumulator comprisesan upper body including the first accumulator pole and a lower bodyincluding the second accumulator pole, both bodies assembled togetherdefining an internal accumulator space volume, a first electrode locatedwithin the internal space of the upper body, a second electrode locatedwithin the internal space of the lower body, a separator dividing thefirst electrode from the second electrode and a seal disposed betweenthe upper body and the lower body for electrical insulation of the firstaccumulator pole from the second accumulator pole.

According to still further embodiment the lithium accumulator includestwo marginal sets and at least one internal set each of said setscomprising first electrodes, second electrodes, separators, currentcollectors and accumulator poles, further comprising: a hollow marginalupper body having an closed external surface and an opened internalsurface to define a marginal frame for receiving a first electrode, ahollow marginal lower body having an closed external surface and anopened internal surface to define a marginal frame for receiving a firstelectrode, internal frames for receiving first electrodes, internalframes for receiving second electrodes, separators disposed between theadjacent first electrodes and second electrodes, current collectors forproviding electrical contact with the first electrodes and connected tothe first accumulator pole, current collectors for providing electricalcontact with the second electrodes and connected to the secondaccumulator pole, at least one internal set of the same configuration asthe marginal sets wherein the marginal bodies are replaced by theinternal frames.

According to one method of production of the lithium accumulator, atleast one bulk sheet of a first electrode, a separator and at least onesheet of a second electrode are stacked by pressing upon each other, theaccumulator body is filled with an electrolyte, closed up and thecurrent collectors of the same type of electrodes are connected.

Alternatively, the individual sheets may be gradually pressed one uponthe other by an impact.

In another alternative, the compressed sheets of at least one electrode,a separator and at least one another second electrode are alternativelystacked on top of each other, the accumulator body is filled with theelectrolyte, closed up and the current collectors of the same type ofelectrodes are connected.

As to the chemical composition it is possible to use only activematerials with a fast lithium ion electro-diffusion for this type oflithium cells (absorbing and extracting lithium very fast). The optimalare spinel structures, which can absorb and extract lithium fast in allcrystalline orientations. It is possible to conveniently use doped orundoped spinels of lithium manganese oxide LiMn₂O₄ (LMS),LiMn_(1.5)Ni_(0.5)O₄ (LNMS) or lithium titanium oxide Li₄Ti₅O₁₂(LTS).

The morphology of the active materials in the powder form, capable toabsorb and extract lithium fast, plays an important role and must meetseveral basic parameters. The optimum particle size of active materialsmay vary, but it must fulfill the ability of complete charge anddischarge (absorption and extraction of lithium ions) of the particleswithin 20 minutes. The optimal are particles of the active materials,which can be completely charged and discharged in less than 1 minute,preferably in several seconds. Advantageously, nano sized crystals ofthe spinel structures may be used. Lithium titanium oxide with thespinel structure and particles size 200-250 nm can be charged ordischarged during 30 minutes, but the same material with the particlessize 30-50 nm can be charged or discharged in the time period up to 30seconds. The lithium manganese oxide spinel with the particles size of150 nm can be charged or discharged in 1 minute.

In the optimum case, the active nano-crystalline materials havemorphology of hollow spheres with the wall thickness up to 10micrometers, preferably from 1 to 3 micrometers. This morphology can beconveniently prepared by spray-drying of the active materialsuspensions. The diameter of these hollow spheres is preferably from 1to 50 micrometers.

When using compact aggregates or agglomerates of the active material,which are made for example by grinding a dry material, the size of theseformations must be less than 30 micrometers, and favorably less than 5micrometers.

The thickness and capacity of the individual electrodes of the lithiumaccumulator according to the invention is at least 5 times, and commonlytwo orders of magnitude higher than the thickness of electrodes used inthe lithium cells with the thin-film planar configuration. Consequently,the lithium accumulator according to the invention enables to achievingup to 5 times higher voltage than the lead accumulator, while keepingthe same capacity and size.

The metal accumulator body of the disclosed construction enables easycooling and heating of the accumulator. If a negative lithium electrodeis used instead of the commonly used graphite electrode, it is possibleto charge the accumulator faster with a higher electrical potentialdifference. The lithium accumulator according to the invention may becharged and discharged in the time interval of 1-24 hours, while 50% ofthe cell capacity can be typically discharged in less than 2 hours. Itis possible to charge and discharge the lithium accumulator 100 timesand more, while preserving 80% of its capacity. The use of the metallithium in the form of dendrites significantly increases the currentdensity compared to a compact lithium foil.

In the process of manufacture, the active material is homogenously mixedwith the highly electron conductive component, for example conductivecarbon. The ratio of the active material to the conductive carbondiffers with the individual chemical compositions. The mixture usuallycontains 40-85 wt % of the active material. Most frequently, the contentof the conductive carbon is 25-40 wt %. This mixture does not containany organic binding agents such as polyvinylidene fluoride (PVDF) orothers. The obtained mixture is compressed into a sheet 0.5-50 mm thick.The sheets of the separator and the second electrode are graduallypressed onto the sheet of the first electrode; the accumulator is filledwith an electrolyte and closed up. The separator to be incorporated intothe accumulator may have an initial structure of a powder which may bepressed down directly onto the electrode or it can be a compact block ofa separately compressed powder to obtain a tablet in a shape fitting therespective shape of the electrode, and may be further subjected to aheat treatment. The thickness of the separator is ranging from severaltenths of micrometers to several millimeters.

If larger blocks of electrodes with higher capacity are manufactured, itis possible to add a current collector to the mixture of the electronconductive component and the active material e.g. wire, metal sawdust,fibers, grid or net in order to carry high currents, and press themtogether into a compact block of the electrode in the way that thecurrent collector is connected to the pole of the electrode. The pole ofthe electrode, electrically connected to a peripheral wire, is usuallythe electrode casing, made of aluminum or another conductive material.Aluminum, copper, silver, titanium, gold, platinum, silicon or otherconductive metals, which are stable in the applicable voltage range, maybe used as this current collector material. It is also possible to usecarbon fibers and nanotubes. The mixture is pressed together,pertinently with an impact into a sheet or block up to severalcentimeters thick. The porosity of an electrode prepared in this wayvaries from 25 up to 80%, typically from 30 to 50%.

A multi-electrode lithium accumulator with a high energy storagecapacity may be advantageously produced by pressing individual sheets ofelectrodes and separators repeatedly on the top of each other andconnecting the poles of the same type of electrode i.e. by repeating theconfiguration of a positive electrode three-dimensional block separatedby a separator from lithium or a three-dimensional block of the negativeelectrode and by electrical connecting of the respective electrodestogether.

The production of the accumulator cell by pressing the individualcomponents from powders is straightforward and inexpensive. Thesemethods also guarantee an excellent resistance against shaking andvibrations, to which the accumulators may be exposed during theoperation.

The lithium accumulator according to the invention is designed for theuse as a high capacity button cell accumulator or for a high voltageaccumulators used in the car industry or as an energy storage medium.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic sectional view of one embodiment of a lithiumaccumulator;

FIG. 2a is a schematic view of the powder mixture;

FIG. 2b is a scanning electron microscope micrograph showing the optimalmorphology of a powder mixture of the active material and the conductivecarbon for a three-dimensional electrode;

FIG. 3 is a graph with voltamograms showing the characteristicpotentials of active materials Li₄Ti₅O₁₂ (LTS), LiMn₂O₄ (LMS), aLiMn_(0.5)Ni_(0.5)O₄ (LMNS) against lithium;

FIG. 4 is a graph showing the characteristics of Li/LTS accumulator (1.5V) discharging cycle at the constant bias of 3 V;

FIG. 5 is a graph showing the current characteristics of Li/LTSaccumulator (1.5 V) during charging and discharging measurements,described in example 2;

FIG. 6 is a graph showing the voltage characteristic of Li/LTSaccumulator (1.5 V) during charging and discharging measurements,described in example 2;

FIG. 7 is a graph showing the current characteristic of LTS/LNMSaccumulator (3 V) during charging and discharging measurements,described in example 3;

FIG. 8 shows a photograph of nano-particles of the active materialLiMn₂O₄ (LMS), used in example 4, acquired by an electron microscope;

FIG. 9 is a graph showing the current characteristics of Li/LMSaccumulator (4.3 V) during charging and discharging measurements,described in example 4;

FIG. 10 is a schematic sectional view of another embodiment of a lithiumaccumulator;

FIG. 11a shows pulse discharge and slow charge characteristics of anaccumulator described in example 5;

FIG. 11b shows a detail of the pulse discharge characteristics duringthe first 30 seconds and switching to the slow charge;

FIG. 12 shows charge and discharge characteristics of an accumulatordescribed in example 5 at different applied biases;

FIG. 13 is a schematic sectional view of still another embodiment of alithium accumulator;

FIG. 14 shows time related charge and discharge characteristics of anaccumulator described in example 6;

FIG. 15 shows a galvanostatic cycle of an accumulator described inexample 6;

FIG. 16 shows a short-circuit discharge of an accumulator described inexample 6;

FIG. 17 is a schematic exploded perspective view of a lithiumaccumulator assembly consisting of multiple electrodes.

DESCRIPTION OF PREFERRED EMBODIMENTS

Reference is now made in details to the embodiments of the presentinvention, examples of which are illustrated in the accompanyingdrawings and in specific examples of these embodiments wherein likereference numbers refer to the like elements throughout. The followingexamples illustrate but do not limit the present invention. It is to beunderstood that where a term three-dimensional (3D) is used throughoutthe specification in relation to electrodes, this term shall refer tothe electrode thickness greater than 0.5 mm

EXAMPLE 1

FIG. 1 shows one of possible embodiments of a lithium accumulator, basedon three-dimensional electrodes, consisting of a hollow body 6 with anopened upper part and a lower part. The lower part if filled up with thematerial of a first (positive electrode) 1, while in the upper part asecond electrode 2 as a negative electrode is located. A separator 5 isplaced above the first electrode 1 to separate it from the secondelectrode 2. The first electrode 1 is in electrical contact with thebody 6 which is the positive pole of the accumulator. The secondelectrode 2 is electrically separated from the body 6 by an insulatingfiller 8 made of corundum. In the upper part, the internal space of thebody 6 is hermetically sealed by an electrically conducting cap 7 madeof copper, and a sealing cover 9 made of plastics. The cap 7 is inelectrical contact with the second electrode 2 and represents thenegative pole of the accumulator. The whole internal space of theaccumulator body 6 is filled with an electrolyte and hermeticallyclosed.

Hereinafter, the composition of individual components of theaccumulator, including the methods of their preparation is described indetail. The schematic drawing in FIG. 2a shows a mixture of powders ofthe active material 4, i.e. nano-crystals of lithium titanium oxideLi₄Ti₅O₁₂ (nano-LTS) and an electron conductive component 3. Themorphology of the mixture is shown by a SEM photograph in FIG. 2b . Theactive material was prepared by drying a suspension of nano-LTS crystalsin a spray drier. The powder was homogenously mixed with a conductivecomponent 3 i.e. highly conductive carbon, manufactured by Timcal anddistributed under a product name Super P Li, in a ratio 65 wt % ofnano-LTS crystals to 35 wt % of the conductive carbon. The fullyinorganic mixture, free of any organic binders, was pressed down intothe body 6 to form a tablet of the first electrode 1. The thickness ofthe first electrode 1 (LTS electrode) was 4 mm and its overall porosity40%. The average size of the active material particles was 50 nm and theability of the particles to absorb and extract lithium ions in a thinlayer during the complete charging and discharging period was below 1minute. The separator 5 was made of highly porous corundum powder, freeof any organic binders, by pressing the powder down directly onto theLTS electrode. The compressed separator was 2 mm thick and its porositywas 85%. In another method, the separator of the same composition wasapplied in the form of a separately compressed block, placed onto theelectrode.

A pure lithium metal sheet, was used as the second electrode 2, presseddown with the copper cap 7 onto the separator 5 into the spaceelectrically separated from the body 6 by a corundum insulating filler 8and a plastic sealing cover 9. After soaking up the accumulator with theelectrolyte 1M LiPF₆ in EC-DMC (ethylene carbonate-dimethyl carbonate)overnight, the accumulator was hermetically closed and cycled severaltimes so that the lithium dendrites could be formed expanding the activesurface of the negative electrode 2. After achieving the full capacityof the accumulator during a slow charging cycle (lithiation of theactive LTS material), the accumulator was discharged at an applied biasof 1.5 V above the formal voltage of the accumulator (3 V againstLi/Li⁺). The voltammogram of the above described combination is shown inFIG. 3 together with the formal electrical potentials of two otheractive materials used in the following examples.

The characteristic discharging cycle is shown in FIG. 4. The reversiblecapacity of this accumulator was almost 100 mAh/cm³. It took 7 hours toachieve the full capacity. Charging currents were improving duringcycling due to the increase of the lithium concentration in theelectrolyte inside the compressed positive LTS electrode 1 and due tothe creation of Li dendrites on the negative lithium electrode 2. Thedischarging cycle was regularly slowing down, when roughly 80% of thetheoretical capacity of the accumulator was achieved.

The accumulator may be completely charged and discharged during severalhours. Typically, it is possible to repeatedly charge and discharge thecomplete capacity of the accumulator during 3 to 24 hours. Mostfrequently, 50% of the capacity is reproducibly and repeatedly chargedand discharged within two hours and cycling of this lithium accumulatortype exceeds 100 charging and discharging cycles. The lithium electrodeallows using of higher bias during charging compared to a graphiteelectrode.

EXAMPLE 2

A lithium accumulator of FIG. 1 was composed of compressed lithiumdendrites as a negative electrode, and a 2.5 mm thick positive electrodeprepared by pressing the mixture of LTS active material with an electronconductive component—conductive carbon, described in example 1. Theseparator was made of ZrO₂ inorganic fibers with the porosity of 70%. Itwas less than one millimeter thick. The accumulator was then cycled fivetimes to achieve the full capacity of the charging cycle. Thetheoretical capacity of the accumulator was 12 mAh. Afterwards, thecurrent and voltage characteristics of accumulator were measured duringfollowing cycles. FIG. 5 shows the current characteristics during thecontrolled charging and discharging with the applied bias of 1 V aboveand bellow the formal potential of the Li/LTS accumulator, which is 1.5V. The reversible process in both directions ended practically aftertwenty thousands of seconds (5.5 hours). FIG. 6 shows the stable voltagecourse of both cycles up to approximately 80% of the theoreticalcapacity during the galvanostatic charging and discharging with theconstant current of 2 mA.

EXAMPLE 3

The negative electrode of a lithium accumulator in FIG. 1 was made bypressing a mixture of 30 wt % of the conductive carbon with 70 wt % ofthe Li₄Ti₅O₁₂ active material (LTS) having the original morphology ofhollow spheres. The average size of LTS particles was 50 nm. Thepositive electrode was a compressed mixture of LiMn_(1.5)Ni_(0.5)O₄active material (LNMS) consisting of agglomerates, smaller than 5micrometers with the average size of primary particles around 100 nm,and 30 wt % of the conductive carbon. The mixture was compressedtogether with an aluminum wire as a current collector. LNMS activematerial was used in excess of 30 wt % creating a 4 mm thick positiveelectrode. Both electrodes were divided by a 0.5 mm thick separator madeof compressed corundum with the porosity of 80%. The accumulator wasfilled with the electrolyte 1MLiPF₆+EC-DMC. The formal potential of theaccumulator was 3.1 V and it was tested in the voltage range from 2.0 to3.5 V. The plot in FIG. 7 illustrates the current characteristic of onepotentiostatic cycle with the charging and discharging voltage 3.5 V and2 V respectively.

EXAMPLE 4

In preparation of the lithium accumulator in FIG. 1, a mixture of 70 wt% of the LiMn₂O₄ active material (LMS) with the aggregate sizedistribution under 30 micrometers, shown in the SEM photography in FIG.8, and 30 wt % of highly conductive carbon was compressed into a tabletof the first electrode 1. The obtained electrode 1 was over 1 mm thick,its overall porosity was 35% and the capacity was 7 mAh. The separatortablet made of porous corundum was 1.5 mm thick with 75% porosity. Itwas pressed directly onto the positive first LiMn₂O₄ (LMS) electrode 1.The sponge of lithium metal dendrites compressed on the surface of alithium metal sheet was used as the second (negative) electrode 2. FIG.9 shows the current characteristics of reversible charging anddischarging of 40% of the Li/LMS accumulator capacity. It took less than3 hours to reversibly charge and discharge 40% of the capacity atpotentials 4.45 V and 3.9 V respectively.

The graph with voltamograms in FIG. 3 shows voltages of cells obtainablewith the mentioned materials. It is apparent from the graph that it ispossible to create a cell with the average voltage of 1.55 V from thecombination of electrodes made of the lithium and Li₄Ti₅O₁₂ (LTS).Comparing lithium to (LMS), it is possible to create a cell with thevoltage around 4.2 V, while if the nickel doped lithium manganese oxideLiMn_(1.5)Ni_(0.5)O₄ (LNMS) is used, the formal voltage of the createdaccumulator is 4.7 V. If two compounds, LTS and LNMS are combined, it ispossible to create a cell with the voltage 3.02 V (4.62−1.60=3.02).

EXAMPLE 5

FIG. 10 shows another possible embodiment of a lithium accumulator. Theaccumulator body made of aluminum consists of two similar hollowsections: an upper body 6 a and a lower body 6 b. The bodies 6 a and 6 bare joined together to form an internal hermetically sealed hollowspace. A first electrode, as a positive electrode, consists of twosimilar positive electrodes 1 a,1 b each disposed along the internalsurface of the bodies 6 a, 6 b so that the first electrode arranged in a“sandwich” constellation defines a central cavity, in which a separatorconsisting of two plates 5 a, 5 b is located. The plates 5 a,5 b areshaped to form an internal chamber in between, which is filled up with amaterial of a second (negative) electrode 2. The second electrode 2 iselectrically insulated from the bodies 6 a, 6 b by a separator 5.

Two VITON seals made by DuPont, as insulating fillers 8 a and 8 b areplaced between the accumulator bodies 6 a and 6 b hermetically closingthe accumulator. The first pole 11 as a positive pole of the accumulatoris connected to the outside surface of the bodies 6 a, 6 b, while thesecond (negative) pole 22 made of copper wire provided with Tefloninsulation protrudes into the chamber of the second electrode 2, whereit is in electric contact with lithium, and its other end extendsoutside the bodies 6 a, 6 b.

In the following details the preparation, composition and characteristicof the accumulator shown in FIG. 10 and the components thereof aredescribed. The active LiCO_(0.1)Mn_(1.9)O₄ material (LCMS) with thespecific surface of 10 m²/g and the hollow sphere morphology, was mixedwith the highly conductive carbon (Super P Li manufactured by Timcal) inthe ratio 60 wt % to 40 wt %. The mixture was pressed into the bodies (6a, 6 b) forming two positive electrodes. The pressing force was 25 kN.One positive electrode contained 0.4 g of the mixture and the other 0.35g. The electrodes were used together in the ‘sandwich’ assemblypossessing the total capacity of 40 mAh. The positive electrodes in thealuminum bodies were 3 mm thick each with the surface area 0.64 cm²,which gives total of 1.28 cm² in the “sandwich” constellation. Twohighly porous alumina separators 5 a, 5 b were profiled to create a 1 mmhigh chamber for the lithium metal anode—the second electrode 2. Theywere prepared by pressing an alumina powder at 25 kN and a subsequentthermal treatment at 1050° C. for 2 hours. The thickness of eachseparator plate was around 0.8 mm and the porosity greater than 60%. Theprofiled separator plates were placed on the positive electrodes. Thespace between them was filled by a mixture of lithium dendrites with 5wt % of Super P Li conductive carbon spread on a 0.3 mm Li metal foil.

The individual bare strands of the wire were pressed into the lithiumfoil and served as a current collector inside the Li metal negativeelectrode. The other end of the wire was the negative pole 22 of theaccumulator. The accumulator positive pole 11 was an aluminum clampconnecting both bodies 6 a, 6 b of the positive electrodes. The dryaccumulator was filled with the electrolyte 0.5 M LiPF₆ lithium salt inEC/PC/DMC (ethylene carbonate-propylene carbonate-dimethyl carbonate)solvents in the ratio 0.5/0.5/1.

LCMS operates in the window around 4.2 V against lithium. Completecharge and discharge of the material occurred in less than 3 minutes,when measured as a 5 micrometers layer on a conductive glass substrate.The specific capacity of the particular material was determined as 90mAh/g. The accumulator was continuously charged at 4.45 V for 7000seconds to reach 60% of the theoretical capacity. Then the accumulatorwas exposed to ten-second discharge pulses at the controlled potentialsof 2 V, 3 V and 3.6 V. After the 10-second discharge pulses theaccumulator was slowly charged at 4.3 V for 3000 seconds and theprocedure was repeated ten times (FIG. 11a ). Details of the step-pulsecontrolled discharge are shown in FIG. 11b . During the 30 seconds0.85-0.95% of the accumulator capacity was discharged.

Behavior of the accumulator, especially signs of a short circuit werefurther observed at 2V, 3 V and 3.6 V discharge and 4.15 V, 4.3 V and4.45 V charge potentials (FIG. 12). The accumulator was taken apart andanalyzed after 70 cycles. The separator showed no sign of penetration ofthe lithium dendrites under the surface. The lithium foil partiallyconverted into a dense black aggregated sponge consisting of Lidendrites. The dendrites held mechanically well together.

EXAMPLE 6

FIG. 13 shows another possible embodiment of a single cell lithiumaccumulator. Similar to the accumulator in FIG. 10, the accumulatorbody, made of aluminum, consists of two analogous hollow sections: anupper body 6 a and a lower body 6 b. Unlike the previous embodiment, thehollow space of the upper body 6 a is filled with a material of a firstelectrode 1 as a positive electrode and the hollow space of the lowerbody 6 b is filled with a material of a second electrode 2 as a negativeelectrode. The bodies 6 a and 6 b are provided with their correspondingpoles i.e. the upper body with the first pole 11 as a positive pole andthe lower body 6 b with the second pole 22 as a negative pole. The firstelectrode 1 and the second electrode 2 are mutually separated by aseparator 5 and the upper body 6 a from the lower body 6 b by aninsulating filler 8.

The preparation, composition and characteristics of the accumulator andits components shown in FIG. 13 are apparent from the followingdescription.

The active LiCo_(0.1)Mn_(1.9)O₄ (LCMS) material with the formalpotential of 4.2 V against lithium, specific surface of 10 m²/g and thehollow sphere morphology was mixed with the highly conductive carbon(Super P Li manufactured by Timcal) in the ratio 60 to 40 wt %. Themixture was pressed into the aluminum upper body 6 a, forming thepositive electrode. The pressing force was 15 kN. The positive electrodecontained 0.736 g of the mixture with the total capacity of 39 mAh. Thepositive electrode was 3 mm thick and its surface area was 1.33 cm². Thenegative electrode was created in similar manner by pressing 0.4 g of amixture containing 60 wt % of the active lithium titanate materialLi₄Ti₅O₁₂ (LTS) in a micronized form and 40 wt % of the highlyconductive carbon (Super P Li) into the aluminum lower body 6 b.Pressing force of 15 kN was applied. The electrode was 2 mm thick andits surface area was 1.33 cm². The theoretical specific capacity oflithium titanate is 175 mAh/g and its formal potential against lithium1.6 V. The capacity of lithium titanate in the negative electrode wasmatching the capacity of LCMS in the positive electrode. The electrodesseparated by a separator 5 made of a bulk layer of alumina powder with95% porosity and pressed directly onto the electrodes formed the dryaccumulator. The separator sheet was few hundreds of micrometers thick.The aluminum bodies also served as the positive and negative poles ofthe accumulator. They were insulated from each other with an insulatingfiller 8—Teflon seal. The accumulator was filled with the electrolyteconsisting of 0.9M (CF₃SO₂)₂NLi+0.1M LiBF₃ lithium salts dissolved inγ-Butyrolacton (GBL)+Propylene Carbonate (volume 0.9/0.1). Then theaccumulator was hermetically closed.

The capacity of the accumulator was 39 mAh and its formal voltage 2.5 V.The accumulator was charged at 2.9 V and discharged at 1.9 V in seriesof 10 cycles. The charge/discharge time intervals were 7000 and 15000seconds and capacity exchanged in the short interval was consistentlyaround 40%. A plot of the third cycling series is shown in FIG. 14 withthe corresponding values organized in the following Table 1

Cycle Capacity (mAh) % Capacity 2.9 v/7000 s - c1 15.7  40% 2.9 v/7000s - c2 −15.4 −40% 2.9 v/7000 s - c3 15.7  40% 1.9 v/7000 s - c4 −16.0−41% 2.9 v/15000 s - c5 22.5  58% 1.9 v/15000 s - c6 −20.4 −53% 2.9v/7000 s - c7 15.3  39% 1.9 v/7000 s - c8 −14.7 −38% 2.9 v/7000 s - c915.1  39% 1.9 v/7000 s - c10 −14.5 −37%

FIG. 15 illustrates a galvanic cycle in the potential range from 1.5 to3 V. Charge and discharge by constant current +/−4 mA demonstrated 30%exchange of the accumulator capacity in 3 hours. Finally, both poles ofthe accumulator were interconnected and short circuit currents weremeasured. The discharge proceeded in one-minute pulses, with relaxationperiods 1, 2 and 5 minutes as posted in FIG. 16. Voltage parameters inFIG. 16 indexing the start and end of the discharge cycles indicate aflat and stable discharge with a small voltage drop and fast relaxationof the accumulator. Thirty percent of the accumulator theoreticalcapacity was discharged in 6 minutes.

EXAMPLE 7

An example of a multi-electrode accumulator according to the inventionis shown in FIG. 17. The accumulator is illustrated in exploded view,i.e. before the individual components were pressed down together to formthe final form of the accumulator. The accumulator was assembled fromthree sets arranged in a stack configuration between an upper body 6 aand a lower body 6 b. Each set comprises two first electrodes 1 a, 1 b,two second electrodes 2 a, 2 b, and two separators 5 a, 5 b. Thematerial of the first electrode 1 b is pressed into an inside chamber ofa lower body 6 b and the material of the other first electrode 1 a intoa frame 10 a. The material of the second electrode 2 b is pressed into aframe 20 b and the material of the other second electrode 2 a inters aframe 20 a. The electrodes 1 b and 2 b are divided by a separator 5 band the electrodes 1 a and 2 a by a separator 5 a. A current collectorfoil 221 is disposed between the second electrodes 2 a and 2 b to form acontact for a wire of a negative pole 22 and a current collector foil111 disposed between the other first electrode 1 a and the next firstelectrode of the superposed set, to form a contact for a wire of apositive pole 11. The second set has a similar configuration as a firstset with the exception that the body 6 b is replaced by a frame of thesame shape as the frame 10 a and that the third set with the upper body6 a is a mirror image of the above described first set. All three setsarranged between the bodies 6 a, 6 b were filled with an electrolyte andpressed down to fit tightly together and hermetically close theaccumulator. The thickness of each individual electrode in compressedconditions was determined by the thickness of the frame and size of thechambers in the bodies, which all were 3 mm. The foils and theseparators were 30 micrometers thick each. Considering that theelectrode surface area was 5 cm², the inside volume of the accumulatorwas approximately 18 cm³. It is obvious that the number of sets stackedon each other is not limited and may be designed in accordance with thedesired capacity of the accumulator. Any combination of electrodematerials described in the preceding examples or materials described inthe description of this invention may be used for the accumulatoraccording to this example.

INDUSTRIAL APPLICABILITY

The three-dimensional construction of repeatedly chargeable lithiumaccumulator cell in combination with the metal lithium as a negativeelectrode, according to the invention, is usable for the simplificationof lithium accumulator manufacture, enhanced capacity, decrease ofdimensions, weight and cost and improvement of safety. This type ofcells is suitable for replacing today's lead-acid accumulators with ahigher voltage system, namely in the automotive industry, for thehand-held electrical tools and portable electrical and electronicappliances and devices, and it also increases the capacity of buttonlithium accumulator cells.

The invention claimed is:
 1. A method of producing a lithium accumulatorincluding at least one cell including a first electrode provided with afirst current collector and connected to a first pole and a secondelectrode provided with a second current collector and connected to asecond pole, the first electrode and the second electrode beingseparated from each other by a separator, the method comprising stepsof: preparing a material of the first electrode from a fully inorganicmixture of dry powders of a first electron conductive component and afirst active material free of organic binders and with the ability tocompletely absorb and extract lithium ions in the time interval of up to20 minutes in the presence of electrolyte and having the morphology ofhallow spheres with a wall thickness of maximum 10 micrometers, or amorphology of aggregates or agglomerates of maximum 30 micrometers insize, pressing down the mixture of dry powders to form a first electrodeof minimum thickness of 0.5 mm and porosity of 25 to 90%, preparing apowder of electrically insulating ceramic material free of organicbinders, pressing down the powder to form a separator with open pores,and porosity of 30 to 95%, preparing material of the second electrodeselected from the group consisting of a compressed, homogeneous mixtureof dry powder free of organic binders of second active material and asecond electron conductive component, metal lithium in the form of alithium sheet or a foil, compressed lithium sheet or foil and dendritesthereof, using the material of the second electrode to form the secondelectrode of minimum thickness of 0.5 mm and porosity of 25 to 90%,providing the first electrode with the first current collector and thesecond electrode with the second current collector, completing the cellby joining the first electrode, the separator and the second electrode,and connecting the current collectors, and encasing the completed celltogether with an electrolyte comprising a non-aqueous solution of alithium salt in an organic polar solvent into the accumulator body. 2.The method of producing the lithium accumulator of claim 1, wherein themixture of dry powers for the first electrode is pressed down into afirst frame made of a conductive metal and the material of the secondelectrode is placed into a second frame made of a conductive metal. 3.The method of producing the lithium accumulator of claim 1, wherein thepowder of the first and second active material is prepared by drying asuspension of nano-crystals in a spray drier.
 4. A method of producingthe lithium accumulator according to claim 1, wherein at least one layerof a first electrode, the separator and at least one layer of a secondelectrode are stacked up by pressing upon each other, the accumulatorbody is filled with the electrolyte and closed up, the first currentcollector is connected to the first electrode, and the second currentcollection is connected to the second electrode.
 5. The method of claim4, wherein the individual layers are gradually pressed one upon theother by impact.
 6. A method of producing the lithium accumulatoraccording to claim 1, wherein compressed layers of the first electrode,the separator and the second electrode are alternatively stacked on topof each other, the accumulator body is filled with the electrolyte andclosed up, the first current collectors is connected to the firstelectrode, and the second current collector is connected to the secondelectrode.